Electro-mechanical machines are widespread. Rotating electro-mechanical machines, such as dynamoelectric machines (generators and alternators) and motors, are particularly prevalent. Rotating electro-mechanical machines usually include a stationary member, known as a “stator,” and a rotating member, known as a “rotor,” which turns in relation to the stator. In certain types of machines, the rotor (sometimes referred to as an “armature”) rotates within the stator (or “field”), which produces a rotating magnetic field. In other types of machines, the rotor produces a magnetic field, which produces an electrical current in the stator.
One common rotating electro-mechanical machine design is the Lundell, or “claw-pole,” design. In a claw-pole machine, the rotor includes claw-shaped pole segments (usually a pair of segments) located around one or more field windings. The pole segments have claw-shaped magnetic poles (or roots) and are affixed around the winding such that the claws mesh together. FIG. 1 shows a conventional claw-pole rotor assembly 100 used in an alternator. As illustrated, a pair of claw-pole segments (110) surround a field winding (120) and the claws (112) of the segments (110) intermesh.
Adequate and proper cooling of claw-pole machines is vital to ensure proper and prolonged operation. Internal cooling fans are commonly used to cool claw-pole machines. Referring again to FIG. 1, rotor assembly 100 includes two internal cooling fans (131, 132). Internal cooling fans, such as fans 131 and 132, are usually attached to the pole segments by welding or frictional clamping.
Conventional internal cooling fan attachment techniques are deficient in a variety of aspects. With conventional techniques, the choice of internal cooling fan material is restricted. For example, in order to weld a fan to a pole segment, the fan must be formed from a suitable material, such as steel. Further, conventional attachment systems may be prone to fatigue and/or failure. Clamps and welds may degrade and eventually fail during prolonged operation. In addition, present attachment techniques do not account for fan alignment.
In addition, conventional internal cooling fan designs are deficient in a variety of aspects. Conventional fans are typically designed with symmetric fan blades that align with the machine segment claws. These symmetric fan designs tend to drive irritating tonal noise. To improve the sound signature, staggered fans are often used. Staggered internal cooling fans utilize asymmetric spacing between blades, which reduces tonal noise, relative to symmetric designs. Staggered fans, however, cannot be aligned with the segment claw roots. This reduces the airflow realized along the rotor axis of the machine.